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Before You Begin

Think! Trains Approaching

I do know some very good designers of signalling systems and the recommendation of a very senior one upon looking at my layout was, "You need three". Now this is not to say that I don't have more than that on my railway but the fact remains that after having studied what he meant I have to admit that he was right. Large complex gantries crusted with cranks and levers may look great -but the problems begin with the production and servicing of the system.

The basic rule I am going to suggest is that you have enough and no more. You are going to have to fight with the weather, squirrels and cats before anything else. The last thing that you want to do is have laboured mightily only to find a knawed off stump the next day... If you are using semaphore signals then it is quite legal to have the "Distant" yellow arm permanently fixed at "Warning". There are several books on the history of signalling and I would advise buying one before starting out on this path.

Two Centuries of Railway Signalling.
Railway Signalling and Track Plans.

It is only in the 20th century that signals became recognisable as signals. The GWR had some wonderfully strange ones and the GNR ones that did somersaults... The Slotted Post three colour ones as used by the NER do have the same problem as the originals.

In real life the signals used to be 1/4 mile apart, here expect them to be about 30 feet apart at most. This means that your system does not have to be as mechanically robust as in real life -it has to be better than that.

You may come across the mapping convention that is used for signalling. The signal follows the direction of the track it is supposed to guard thus they can seem to be at very strange angles. Feel free to use vertical ones if this makes your drawing more readable to you. How you utilise your signals is dependant on the era that you are "in". Semaphore signals operated by a signal man would have gone to from Danger to Clear in front of the locomotive and then returned to Danger after it had passed. Modern colour aspect signalling uses Clear running and only uses Danger after the loco has passed.


Victorian signals were by and large ODD. They came from differing companies and ideas on how they should function. The NER three colour three aspect slot post signal was the first contender for a Standard Design. However it suffers from the problem of the slot. For those who do not know the "Abbots Ripon" railway disaster was directly caused by this design. It snowed, the snow collected in the slot and froze to ice, trapping the signal in the slot. The signalman pulled the levers, but the cranks bent and broke off. Thus the Signal was permanently at "Right of Way" and both the Scottish express and the approaching coal train ASSUMED they could carry on...

After the Inquest into this the mandated design is what we now called the Lower Quadrant. The kerosene lamp fitted at the back of the Signal Glass had a small amount of salt added to it to prevent the water that collected in the kerosene reservoirs from freezing and splitting the sides. This lead to very yellowish flame. This explains why the Glasses are Red and Blue, if you are going to illuminate your signals with lights then you would need a yellowish LED of around 585Nm wavelength or wheat bulb with a flame temperature of around 4500F -depending on the supplier preference...

The end of the Edwardian Era and WW1 lead to a range of experimental designs. The Two Aspect Searchlight colour signal may be found here. The next great changes deal with the Big Four. Upper Quadrant signals arrive and some of the Big Four identifiers. The Southern Railway got the worst of a Bad Deal. Of the companies that formed it, all but one were in receivership. This meant it was strapped for cash for several decades. Thus Southern did things on the cheap. The classical early cheapo design used two length of old rail as the post -some applause should be given as several of these are still around in the Chatham docks area!

The birth of BR brought the demise of the Semaphore Signal. These were replaced first by two aspect Green and Red, then three aspect Green Yellow Red, then four aspect and finally five aspect for 140mph running.

How Far Do I Go?

It is possible to have a perfectly signalled layout and for it be far too complex for one person to operate and run trains with. Most of the time it is going to be you who are both signalman and driver. As far as possible either automate or simplify as much as you can. You will have to accept that things cannot be true -but there is nothing stopping you getting as close to the original as possible. You may purchase from Australia a kit of parts to assemble your own Victorian style "Tappet and Slide" locking frame. The finished item may be classed as a work of art but it is not an easy option. The HG method of using chords and stop tabs on the ends of the levers does work well -but is intensely difficult to get "exact". When the R.O.D took over the "Romney Hythe and Dimchurch" 15" scale railway designed by him, they took a sledge hammer to the system, then installed a tappet and slide...

These will connect to DIY cranks and rollers and I have used them myself. These are the ones from Cliff Barker. There could be a slight problem in the length of the "stub", which is short and may not penetrate the layer of roofing felt.

Similarly I am constructing a 1910 style electro-mechanical signalling system that is a copy of the type that I "grew up" on. It is going to be a challenge. This is a working clone of the Westinghouse Type "L" signalling system. It is based on a combination of "local" and "remote" control. The remote panel sets the signal to RED and the local controls set the preceding signal to DOUBLE YELLOW and YELLOW.

The MERG organisation sell modules that may be linked together to provide a fully interlocked system. BUT they expect you to understand quite a high level of construction.

Some of you may have come across the book "Model Railway Electronics" by Roger Amos, which is mainly for 00 scale systems. However with some thought it is possible to ramp up the electronics to G3 power requirements. I have a copy of the second edition. The local electronics shop is not sure if some of the core ICs are still available. Anyone capable of reading the last half of the book will be able to figure out modern replacement digital ICs.

Model Railway Electronics. Roger Amos - still very common.
Model Railway Signalling. C.J.Freezer - getting rare.
Railway Signalling and Track Plans. R.Essery -still very common
British Railway Signalling in Colour: For the Modeller and Historian. R.Powell Hendry -getting hard to find but still around.

The advent of the Raspberry PI and the Arduino have raised the concept of complete automation schemes. The standard languages fitted to these devices is not "powerful" enough to manage the job in my opinion. If you are a competent enough programmer to use a PI or an Arduino then you would probably use a PC "High Level" language based system.... However it is now possible to have "Wolf Packs" of PIs in multiples of four providing the raw processing power required. The main limitation still remains that there is not a "High Level" language suitable, but some "Machine Orientated" low level languages are powerful enough for the PI/Arduino to use.

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Page last modified on March 01, 2018, at 07:08 AM